Electric motors are nowadays employed for a plethora of different applications in essentially all fields of technology. Depending on the actual use of the respective electric motor, various types and various sizes of electric motors are employed.
As an example, if an electric motor has to be used for an application where a constant turning speed of the electric motor can be used or is even required, a synchronous electric motor without a commutator can be used, in particular if alternating current is available. However, a start-up of such an electric motor might be difficult if a load with large moment of inertia has to be driven.
If, however, a variable turning speed of the electric motor has to be provided (and additionally in the case of a direct current source), the traditional approach was to use electric motors, comprising a commutator (so called asynchronous electric motors). A problem involved with such commutated electric machines is the commutator, since this is a component that is particularly subject to a non-negligible wear. Furthermore, when using a commutator, typically sparks occur when the electric motor is turning. Such sparks can render the resulting electric motor unusable for certain applications, in particular if flammable gases are around, unless additional precautions are taken.
With the advent of modern semiconductor-based power electronics, the use of synchronous electric motors, in particular synchronous reluctance electric motors, have become more and more widespread. With such synchronous electric motors, commutators can be dispensed with. Furthermore, by providing an alternating electric current with a variable frequency, a synchronous electric motor can be driven at essentially any rotating speed. Even changes in turning speed can be realised. This has made possible certain applications that were hard to achieve, if at all, beforehand.
With increasing number of electric motors and increasing energy prices the problem of efficiency becomes increasingly important. Efficiency does not necessarily relate only to the consumption of electric energy with respect to the mechanical power generated by the electric motor. Instead, it can also relate to the size (volume) of the electric motor that is necessary to achieve a certain mechanical power level.
Although a number of different controllers for electric motors, a variety of electric motors and a variety of methods how to drive an electric motor are known in the state of the art, there is still a necessity for further improvements.